The present study was designed to test the hypothesis that estrogen receptors (ER) in the blood vessel wall play a role in the modulation of the release of endothelium-derived nitric oxide (EDNO). Both basal and stimulated release of EDNO were determined in aortic rings isolated from female and male wild-type and male homozygous estrogen receptor knock-out (ERKO) mice.125 I-17 ␤ -estradiol binding in aortic tissue showed significantly more high affinity cytosolicnuclear-binding sites in male compared with female wildtype mice. Estrogen receptor transcripts were present in the aorta of male wild-type mice, but they were absent in male ERKO animals. Basal release of EDNO (determined by endothelium-dependent contraction caused by N G -nitro-Larginine) was significantly higher in aorta of wild-type male mice compared with wild-type female mice, and significantly lower in the aorta of male ERKO compared with male wild-type mice. Acetylcholine-induced endotheliumdependent relaxation was similar in all groups studied. No difference was observed in the activity of calcium-dependent nitric oxide synthase in homogenates of lungs and brain taken from male wild-type and ERKO mice. These studies show a significant association between the number of estrogen receptors and basal release of EDNO in the aorta of mice, and suggest that decreased vascular estrogen receptor number may represent a novel risk factor for cardiovascular diseases.

1 Guanosine 3': 5'-cyclic monophosphate (cyclic GMP) release and vascular tone was measured in the isolated kidney of the rat perfused at constant flow with Krebs-Henseleit solution. The effects of 3 vasodilators, acetylcholine (ACh), atrial natriuretic factor (ANF) and sodium nitroprusside (SNP) on the renal release of cyclic GMP and vascular tone were examined. The ability of the endothelial-derived relaxing factor (EDRF) inhibitors, haemoglobin and gossypol, to modify vasodilatation and vasodilator-induced changes in cyclic GMP releases from the kidney was also investigated. 2 Renal cyclic GMP release was elevated 8 fold by ANF (0.01 pM), 5 fold by SNP (1 pM) and 3 fold by ACh (0.3 yM).3 For ACh, both the increase in renal cyclic GMP release and the vasodilatation were reduced by the EDRF inhibitors, haemoglobin (1 pM) and gossypol (15 pM). For SNP, neither the increase in renal cyclic GMP release nor vasodilatation were inhibited by gossypol (15 yM).4 For ANF, neither the increase in cyclic GMP release from the kidney nor its vasodilator activity were affected by haemoglobin (1 pM).5 EDRF inhibitors reduced the basal release of cyclic GMP from 0.32 + 0.06 pmol min ' to 0.18 + 0.03 pmol min-1, gossypol being more effective than haemoglobin. 6 The results are consistent with the ability of ACh to induce EDRF-mediated vasodilatation in the isolated perfused kidney of the rat. Basal EDRF release appears to contribute approximately 50% to the basal release of cyclic GMP from this preparation. The renal vasodilator action of ANF however, is independent of EDRF, although the renal vascular endothelium cannot be discounted as a site at which ANF stimulates cyclic GMP production.

1. The sensitivity of the kidney to endothelium-derived-relaxing-factor-mediated vasodilatation has been investigated in the spontaneously hypertensive rat and the Wistar-Kyoto normotensive rat using an isolated perfused rat kidney model. 2. No difference in the slope, ED50 or maximum of the concentration-response curves for the endothelial-dependent vasodilators A23187, a calcium ionophore, and acetylcholine could be demonstrated between kidneys obtained from the spontaneously hypertensive and the Wistar-Kyoto normotensive rats. 3. No difference in the slope or the ED50 of the concentration-response curve for the endothelial-independent vasodilators, atrial natriuretic factor and sodium nitroprusside, could be demonstrated between kidneys obtained from the spontaneously hypertensive and the Wistar-Kyoto normotensive rats. However, in the spontaneously hypertensive rats, the maximum vasodilator response to atrial natriuretic factor, but not to sodium nitroprusside, was increased. 4. The perfused kidney from the spontaneously hypertensive rat also showed an increase in the maximum but not in the slope or ED50 of the concentration-response curve for vasoconstriction induced by the alpha 1-adrenoceptor agonist methoxamine. 5. The involvement of endothelium-derived relaxing factor in mediating the renal vasodilator response to A23187 and acetylcholine was confirmed in experiments performed in perfused kidneys obtained from normotensive Wistar rats. 6. It is concluded that the sensitivity of the kidney to endothelium-derived-relaxing-factor-mediated vasodilatation is not modified in the spontaneously hypertensive rat. This does not, however, exclude a role for the synthesis of endothelium-derived relaxing factor in the maintenance of blood pressure in the spontaneously hypertensive rat.

1 X-ray microangiographic techniques were used to study the influence of endothelium-derived relaxing factor (EDRF) on vasomotion in the isolated, intact, buffer-perfused kidney of the rat. The main renal (RO), segmental (R1) and interlobar (R2) arteries (control diameters ca. 600, 400 and 300 gm respectively) were studied quantitatively.2 Inhibition of basal EDRF activity by haemoglobin (1 pM) did not elevate perfusion pressure or constrict R0, R1 and R2 in control preparations, implying a low level of spontaneous myogenic tone. In preparations preconstricted by 0.3 gM methoxamine, haemoglobin caused a further rise in perfusion pressure and amplified constrictor responses in R1 and R2 while also inducing 'paradoxical' dilatation of Ro.3 A spatially heterogeneous pattern of diameter responses (constriction of R2 and R1 with minimal dilatation of RO) was observed with two concentrations of methoxamine (0.3 jM and 3 pM).The magnitude of these responses was, however, smaller with 3 jM than 0.3 gM methoxamine, even though it increased perfusion pressure to a greater extent (88 mmHg cf. 24 mmHg). This 'paradoxical' behaviour indicates more pronounced constriction of distal arteries (which could not be resolved quantitatively) with 3 gM methoxamine.4 In contrast to the heterogeneity of constrictor responses induced by methoxamine, the dilator action of acetylcholine was spatially homogeneous: log ICo values calculated from the diameter changes induced in R0, R1 and R2 were similar and, moreover, equivalent to that calculated from the corresponding alterations in perfusion pressure. The fall in perfusion pressure induced by an approximately median effective concentration of acetylcholine (0.3pM) was completely reversed by haemoglobin, consistent with the involvement of EDRF, although, reversal of the acetylcholine-induced dilatation of R0, R1 and R2 was not observed.5 The results are consistent with the idea that constriction of distal vessels can attenuate and even directionally reverse intrinsic constrictor responses in the proximal R0, RI and R2 'feed' arteries by producing an overriding increase in 'upstream' pressure. This effect explains the paradoxical dilatation of Ro induced by haemoglobin in the presence of 0.3 jM methoxamine, the smaller magnitude of the diameter changes induced in R0, RI and R2 by 3 pM as compared to 0.3 jM methoxamine, and the failure of haemoglobin to reverse the acetylcholine-induced dilatation of R0, R1 and R2.